Some servers in the UK would allow us to keep many images which are allowable under the UK's broad FOP provisions, but which are not allowed in the US.
As far as I know, the location of the servers is not really relevant. It's relevant who runs the servers, and also where the work was created, and where the uploader is located. The "golden rule of thumb" on commons is: it has to be PD in the US, the country of origin (or first publication), and the uploader should check with local laws. I don't think we can get around this.
So, just having a couple of servers in different places wouldn't help - it would have to be a completely separate organization. Which would also mean that images on such servers can't be used seamlessly on Wikipedia, etc.
Trying to interpret copyright law in the context of an international project driven by user created content is a real challenge; sticking with something like the smallest common denominator seems to have worked ok. Trying cheap tricks to work around this ("this image is ok now because the bits are on a different server") will only create an ugly mess, and is also not legally sound, as far as i know. As I said, it would have to be a completely separate, UK based project for "PD in UK only" stuff, having nothing to do with Wikimedia.
But IANAL. I'm just saying that technical solutions to legal problems tend not to work.
-- Daniel